The invention relates to an ink cartridge comprising two short, longitudinally spaced, and transversely extending end plates and two long, longitudinally extending, and transversely placed side plates. A respective doctor blade sheet is on each of the side plates, in particular a doctor blade strip. In such an ink cartridge, the end plates and the side plates form a frame or box which encloses a body of a predetermined volume of ink that can pass through a downwardly open mouth of the ink cartridge, between the outer edges of the two doctor blades, onto a roll of a printer.
Printers and lacquering machines for the printing or lacquering of sheet-like printing substrates have been in commercial use for many years. Because the subject matter of the invention may be used in printers and also in lacquering machines, all descriptions below relate to printers as well as to lacquering machines, without limiting use.
Of these printers, one type operates according to a rotary printing principle, for example a flexographic, offset, letterpress, rotogravure process, etc., in which the print master of the image to be printed is cut into an outer surface of one or more printing cylinders, or in the form of a printing plate is clamped onto the outer surface of a printing cylinder, and during the printing process the print image is transferred, either directly or via a downstream transfer cylinder, to the printing substrate by rolling the printing cylinder over its outer surface.
To this end, the print master on the printing cylinder is inked by one or more inking units so that the ink-transferring areas of the print master are uniformly inked upon each revolution of the printing cylinder, thereby ensuring essentially uniform print quality on the printing substrate.
For uniform print quality, it is crucial that, regardless of the printing speed, the inker continuously supplies the same quantity of printing ink in the form of a homogeneous ink film to an inking cylinder, from which the printing ink is conveyed via the print master to the printing substrate. For producing such an ink film it is common to withdraw a given quantity of printing ink from an ink cartridge, using a anilox roll, for example, by partially immersing the outer surface of the anilox roll in the printing ink provided in the ink cartridge, and when the anilox roll rotates about its cylindrical axis a specified quantity of printing ink is conveyed from the ink cartridge.
To this end, the anilox roll has multiple recesses, for example cups or grooves, on its outer surface which take in the printing ink. Excess printing ink on the outer surface of the anilox roll is advantageously scraped by the downstream doctor blade from the outer surface of the anilox roll when the anilox roll rolls out of an ink cartridge, and the scraped-off printing ink remains in the ink cartridge.
By predetermining the total volume of all recesses or cups in the anilox roll during manufacture thereof, it is possible in each case to take only a specified quantity of printing ink from the ink cartridge. However, for this type of ink withdrawal it is problematic that the ink cartridge is sealed with respect to the anilox roll, in particular in the region of the top surfaces of the anilox roll cylinder, at the end face edges of the doctor blade sheets facing the end plates of the ink cartridge.
Since the doctor blades rest on the outer surface of the anilox roll under pretension, and likewise must follow any imbalance of the anilox roll, it is not possible to fixedly connect the doctor blades to the end plates, so that a gap remains with respect to the end plates through which printing ink can leak out of the ink cartridge.
In particular for ink cartridges situated above the anilox roll, and/or when low-viscosity printing inks are used, there is a risk that printing ink may leak out and pass uncontrolled into the printing unit in unacceptable quantities. It is also common to remove the ink cartridge together with its contents from a printing unit in order to operate a printing unit using another printing ink, or for cleaning or maintenance purposes, for example.
To this end, as disclosed in U.S. Pat. No. 7,234,396 for example, at least one of the doctor blades is displaced along the anilox roll surface in such a way that the outer edges of the doctor blades come to rest one on top of the other and the mouth of the ink cartridge is closed off with respect to the outer surface of the anilox roll. However, for closable ink cartridges of this type or also of other types, there are additional gaps between the end edges of the doctor blades and the end plates, through which printing ink can emerge in an uncontrolled manner.